Verifying OA mix during cooling coil troubleshooting ensures what?

• A. It reduces noise
• B. It eliminates the need for filtration
• C. It ensures the outdoor air percentage for ventilation and performance
• D. It ensures refrigerant charge is correct

Answer: (C)

Outdoor air mixing fraction controls how much fresh air is brought into the system, which directly affects ventilation and overall performance. When you’re troubleshooting a cooling coil, verifying this mix ensures the system is delivering the intended outdoor-air percentage for proper ventilation and efficient operation. If the outdoor-air damper is misadjusted or stuck, you may either under-ventilate, compromising indoor air quality, or over-ventilate, wasting energy and potentially impacting humidity control. The outdoor-air fraction also sets what the coil sees in terms entering air conditions, influencing leaving-air temperature, coil load, and the ability to meet design conditions. The other options don’t fit because noise reduction isn’t controlled by the outdoor-air mix, filtration remains necessary regardless of mix, and refrigerant charge is a separate parameter unrelated to the outdoor-air proportion.